martin



T. G. MARTIN.

TELEPHONE EXCHANGE SYSTEM. APPLICATION FILEDEAPR. n. 1906. RENEWED OCT. 14.1914.

1,19%,389. Patented Aug. 8,1916.

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z z wa m RENEWED OCT-14,1914- Patented Au. 8, 1916.

T. G. MARTIN TELEPHONE EXCHANGE SYSTEM.

APPLICATION HLED APR. 17. 1906.

T. G. MARTIN.

TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED APR. 17. 1906- RE-NEWED OCT- 14, 19M.

1 1 9&3 39., Patented Aug. 8, 1916.

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TALBOT G.MAJR.TIN, OF CHICAGO, ILLINOIS FIRST TRUST AND SAVINGS BANK,

, ASSIGNOR, BY MESNE ASSIGNMENTS, T0

TRUSTEE, OF CHICAGO, ILLINOIS.

TELEIHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented Aug. a, rare.

Application filed April 17, 1906, Serial No. 312,156. Renewed October 14, 1914. Serial No. 866,726.

To all whom it may concern:

Be it known that ][,'TALB0T G. MARTIN, a citizen of the United States of America, and resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in Telephone-Exchange Systems, of which the following is a speclfication.

My invention relates to telephone systems in general, but more particularly to automatic or semi-automatic telephone systems, and especially to automatic telephone systems in which electrically-propelled and step-by-stp-actuated switching machinery is employed at the exchange or central station'for completing connection between calling and called subscribers lines.

As herein described and illustrated, my invention is shown in connection with a system in which selectors and connectors are employed, and in which the current for char ing the subscribers transmitters is supplie from a common] battery or other centralized source of talking current, the same source being also employed for furnishing the electrical current for operating the said selectors and connectors. For the broader purposes of my invention, however, the sub scriber-controlled and automatic switching machinery for connecting calling lines with called lines may be of any suitable, known or approved character, and the current for charging the subscribers transmitters may be obtained from any suitable source or sources, such as local batteries at the subscribers substations.

As will hereinafter more fully appear, my invention is in certain respects an improvement on the automatic common battery telephone system described in my Patent No. 1,185,521, granted May 30, 1916. It will also be seen that in certain respects my invention is in the nature of an improvement on the general type of connector disclosed in Patent No, 815,176, granted March 13, 1906, to Keith, Erickson and Erickson. For the purpose of illustrating my invention the selectors herein shown and described may be of the general type disclosed in Patent No. 815,321, granted March 13, 1906,

to Keith, Erickson and Erickson.

Generally stated, the object of my invention is the provision of an improved and highly eflicienttelephone system, preferably of the automatic or semi-automatic type, of such character that t W ll afiord proved and satisfactory telephone service to the subscrlbers thereof, at the same time taking nto account that a reasonably low cost of installation and maintenance is always, in matters of this kind, an important consideration.

Special objects of my invention are the provision of connectors or other automatic swltchlng machinery having means for automatically applying the ringing or call-signal current to the called subscriber-"s line as soon as the connection between the two lines is fully established, whereby the calling sub-- scriber merely calls the desired number, and is not required to operate button after establishing connection with the called line; the provision of such a construction and arrangement as will permit a connector to lock itself on the called line, regardless of whether the latter is busy or idle, and until the calling subscriber hangs up his telephone, during which time the connector either rings the called subscriber until the latter answers, or in the event that the called line is busy automatically transmits a busy signal to the calling subscriber, the arrangement also being such that the connector can thus lock itself on a busy line without interfering with the conversation already being carried on over such line, and without permitting the calling subscriber to listen-in or overhear such conversation; the provision of an improved trunk-releasing arrangement involving a differential-relay in the talking circuit, preferably at the called side of the condensers or other inductive connections which are associated with the connector and which are located in the talking circuit for the purpose of dividing the same into two inductively-connected portions, as will hereinafter more fully appear; the provision of an lmproved arrangement whereby the ringing-generator can also be employed for supplying the current necessary for transmitting a busy signal to the calling "subscriber when the called line is busy or already occupied; and the provision of certain details, combinations and features of im rovement tending to increase the general e 'ciency and serviceability of a telephone system of this particular character.

To the foregoing and other useful ends, as will hereinafter more fully appear, and as will be apparent to those skilled in the selector A-of the calling line, a connector C' common to the subscribers, and a first-selector A of the called line. Fig. 2 is not only a diagrammatic view of the first selector A,

but a perspective as well, showing the arrangement of the relative parts about the switch-frame, which latter is not shown. Fig. 3 is a similar view of a connectorswitch. Fig. 4 illustrates changes to be made in the connector circuits when the said connector is used in a very small exchange, in which case the calling subscribers lineconductors are connected directly to the connector.

The use of-first-selectors and even of seccud-selectors and other switches commonly used in systems of the general type herein described is not essential. Subscribers may be provided with connectors only, if necessary, as will be hereinafter more fully described.

The substation equipments employed in connection with common battery systems of the nature in question are all of a wellknown and suitable type. Substation #100, for example, is at once recognized by the peculiar switch-hook 2 which is made with a number of cam-like arms 3, 4, 5 and 6. The primary circuit at said station comprises the main line-conductors in series, and contains the primary winding 7 of the induction-coil 8, a transmitter 9, a couple of springs 10 and 11 through the medium of which the said circuit is maintained closed or opened, depending upon Whether the hook is up or down. Said hook is pivoted by a screw 12, and is forced to rise Whenever the weight of the receiver 13 is removed from it, by a suitable switchhook-spring not shown. The secondary circuit comprises the said receiver 13 in series with the secondary winding 14 of the induction-coil 8 in a permanently closed local circuit. The ringer circuit at said substation includes the ringer 15, the ringer circuit springs 16 and 17, and the condenser 18. This circuit, while the switch-hook is down, is closed by the cam-arm 4 that presses the ringer circuit springs 16 and 17 into contact, and is normally bridged across the main line. While the hook is up, however,

the said bridge is open, because the said springs 16 and 17 spring apart after the cam-arm 4 is removed from the spring 16.

'The cam-arm 6 controls the continuity of a ground circuit between the so-called groundpost 19 and the ground terminal G through the medium of two springs 20 and 21 that are included in said circuit. The substation rel' has three other springs 22, 23 and 24 which forced together by the cam-arm 3, which latter then engages the laterally projecting extremity 25 upon the spring 24; The engaging portions of the cam 3 and spring 24 are constructed with their surfaces at an angle to each other, so that when the hook goes down one surface of the projection 25 is engaged, and when it rises the opposite surface comes into use. In this way, when the hook goes down, the spring 24 is forced onto the springs 23 and 22, and when the hook rises it is shoved in the op osite direction. Therefore, at the limit 0 each stroke of the hook the cam-arm 3 clears the spring 24. The calling device employed by the subscriber comprises two push-buttons 26 and 27, two contactoints 28 and 29, two springs 30 and 31 an the so-called groundpost 19. The spring 30 and contact 28 are normally in contact, as well as the spring 31 and contact 29. But when the button 26 is pressed the spring 30 is separated from the contact-point 28 and connected with the ground-post 19, and when the button 27 is pressed the second spring 31 is pressed onto the same ground-post, after said spring 'leaves the contact-point 29.

I vertical or end-wise step-by-step movements occuring first. Among the functions of the shaft is that of a holder for the line-wipers 35 and 36 and the private-wiper 37. The former two comprise a set distinct from the latter, but both sets are located within range of the contacts of their respective banks 32' and 33. Said wipers are not only insulated from the shaft, but from each other as well. Among the details that are associated with the shaft is a 'cam piece 38 which is of a split sleeve design and secured to the shaft by a screw 39. Saidcam abuts on a hub 40 that is shrunk to the shaft near the middle of the latter. This hub carries a set of longitudinal teeth 41 that serve, as will be disclosed, to

enable the forward rotation of the shaft and as a locking means against backward rotation of the same. On the neck portion of respect to the ground-spring 57.

memes said hub there is found a set of circular teeth 42 that serve in turn as a means by which the raising of the shaft is accomplished and for locking it when raised. These circular teeth are traversed by a groove or channel 43 into which the end of a so-called shaft-rest 44 normally projects; but when the shaft is rotated any one of the said circular teeth which may be at the proper height slides onto the endof the said rest. The end of the rest is, of course, adapted to fit the said circular grooves between the ratchet-teeth. The upper surface of the rest is level, but the under side of the end thereof is chamfered to correspond with the upper slope of the circular teeth. Above the hub 40 the shaft carries an arm 45 known as the normal-post-arm and which is, while the switch-shaft is at rest, and while the shaftrest occupies the slot 43, retained against the normal-post 46 by the coiled spring 47. Said normal-post-arm 45 is given control over a switch-shaft-spring 48, so that when the shaft is in normal position said spring is retained in connection with the contact-point 49, but when the shaft is raised said spring leaves the said contact-point 49 and engages instead with the contact-point 50. Among the magnets allotted to the first-selector some are used as relays and others as operating magnets. The magnets 51 and 52 are among the former kind and are known as the vertical and rotary line-relays. By means of their respective armatures 53 and 54 the springs 55 and 56 are controlled with Said springs are comprised in energizing circuits of operating magnets that raise and rotate the shaft. Another relay, known as the bridge-cut-ofi' relay 58, controls through the medium of the armature 59 three springs 60, 61 and 62 that control the connection between the line-relays 51 and 52 and the nongrounded terminal of the central battery B. Also, the magnet 63 with an armature 64 that controls the springs 65 and 66 constitutes the back-release-relay which is used for restoring the switch after it has seized a trunk-line. Of the operating magnets the magnet'67 is known as the vertical-magnet and has a so-called vertical-armature 68 that is supported by pivots 69. Whenever the coils 70 and 71 of said vertical-magnet become energized the armature 68 is attracted, and when the magnetization ceases the retracting spring 72 restores said armature to is normal position. The upward movement of the armature is limited by the pole-pieces of the magnet-coils 70 and 71, and the lower limit 'is marked by a section of the switchframe (not shown) that passes under the arm 7 3. Said arm is known as the verticalarm and extends forwardly from the vertical-armature 68, of which latter'it is a part. The vertical-arm carries on its end a socalled vertical-pawl 74 which, when the ver -tical-armature is attracted, engages with some one of the circular teeth 42 to raise the shaft. Normally the under surface of the upper section of said pawl rests against a piece (not shown) that is secured to the switch-frame and that retains the pawl away from the circular teeth. When the verticalarmature is attracted, as the said pawl rises, a retracting-spring 75 thrusts the upper side of the pawl toward the circular teeth 42. As soon as said pawl clears or disengagesits normal rest, and by the time that the vertical-armature strikes the pole-pieces, the vertical-pawl strikes with the rear surface of its upper section a bumper piece or stop which constitutes a part of the switch-frame. Therefore, the shaft is thus prevented from being thrown up more than one notch at a time by its own momentum. It is clear, then, that the said pawl not only raises the shaft, but that it also acts as a lock at the end of each stroke.

The vertical-arm' also has an L-sha-ped piece 76 on its under edge that projectsv under a so-called release-link 77 of flexible spring material. Said link carries an aperture 78 on its front end, and is secured to the armature 79 of the operating magnet 80 known as the release-magnet. Said armature is suspended from the frame by the supports 81 and normally retained by the spring 82 away from the pole-piece of the releasemagnet. A stop is suitably provided behind said armature to limit its movement when retracted. The first-selector is provided with a peculiarly shaped mechanism 83 known. as the double-dog. It is pivoted so that it may swivel about a vertical axis that passes through the pivots 84. On its front side said double-dog'develops into two dogs 85 and 86 which are so situated and constructed that the former may coiiperate with the circular teeth 42, while the switch-shaft is raised and in normal rotary position, and the latter with the longitudinal teeth 41 when the shaft is rotated. To the right of the pivots 84 the body of the double-dog extends rearwardly, andprojecting down therefrom is an arm 87 that comes into use very prominently during the releasing of the switch. Near the extremity of and on the upper side of said body a pin or lug 88 pro- ]ects upwardly. Said lug is normally caught magnet 67, but as a matter ofconvemence of -the vertical-magnet has its armature 93 itsnew position. The release-link 77, while the double-'dog'vis free, rests with its free endweight.

' upon. the lug 88/ and out of'locking engagement therewith. When the vertical-magnet 5 is e'nergized a second time the shaft is raised I-a second stepandthe dog 85 at the second stroke passes from under the first tooth to below'the second tooth, holding the shaft again as before. The release-magnet 80 is composed of two coils like the. verticalillustration only one coil is shown. If while the shaft is raised the said release-magnet should be energized, the release armature 7 9,

of course, is attracted and the release-link 77 is thrust forward to catch the lug in the pivoted 'in a vertical plane. Said armature may be moved about a vertical axis that passes through the pivots 94. The limit of movement of said armature toward the rotary-magnet is determined by the pole-pieces of said magnet, which movement is produced by the rotary-magnet itself.- The motion of the armature in the opposite direction'is produced by the-retracting-spring 95, and is limited by a switch-stop (not shown) behind the so-called rotary-arm 96. This arm, like the vertical-arm, carries a so-called rotarypawl 97. Similar to the vertical-pawl, said rotary-pawl normally rests against a stop (not shown). that retains it away from the longitudinal teeth, and when the rotaryarmature is attracted it is drawn into en- 1 gagement with the longitudinal teeth by a spring 98 that is attached between-the ro-- jtallyfillm and the rear of said pawl. By the "time that the rotary-armature strikes the i further advance by the force of its own momentum. At the end of the first rotary step Yea.

pole-pieces of the rotary-magnet, the rotarypa'wl'also strikes a bumper-post, as does the vertical-pawl, and locks'the. shaft against the dog 86falls behind the first longitudinal tooth, so that when the rotary-pawl falls back the shaft is retained. It should be evident that as the shaft is rotated the vertical-dog 85 is extricated for a moment from the groove below the circular tooth with which it has been in engagement, by the passageof the rotary-dog 86 across the longitudinal tooth over which it has to slide at the time; but at the beginning of the rotation it will be evident that the tooth which has been caught by the vertical-dog slides onto the shaft-rest 44, and in this way the shaft is still held raised after the rotationbegins. The construction is such that when any one of the circular teeth passes onto its shaft-rest 44 theshaft rises a trifle in order that the tooth that has been resting upon the dog 85- may clear said dog and reduce the friction of the parts during operation.

When the shaft is raised the circulantocth abutting onthe shaft-support 44 is shghtly below the level of the upper surface of the shaft-rest 44, and to enable a rotating tooth 1 to pass onto the shaft-rest 44 the edge of the endthereof, as well as the edge of all circular teeth, are rounded off slightly to enable the rotary-armature 93 to raise the shaft slightly, as stated, without catching.

The rotary-armature is provided with a so-called interrupter-finger 99 that separates the interrupter-springs 100 and 101 whenever the rotary-armature is attracted; also with a rotary-armature-finger 102 that exercises certain controllin influences over the armature of the last 0 the operating magnetsthe private-magnet 103. The said private-armature 104 works about a horizontal axis that passes through the supporting points 105. This armature is formed with a forwardly projecting arm 106, the latter having two flat surfaces in an approximately horizontal plane. Furthermore, the end of the said arm is bent downwardly at right angles and carries certain mechanical details, namely a lateral arm 107 which is designed to control circuits comprising the prlvate-springs 108, 109 and 110, and a tooth escapement which includes two flexible springs 111 and 112, each of which springs is riveted by one end to the arm 106, one on the upper side and the other on the lower. The upper spring is straight and has formed on its end two tooth projections 113 and 114 which extend downwardly, while the lower one is bent down and at right angles again to the front. This double angle on the lower spring is so designed that the latter may clear the bent portion of the privatearm, against which .portion-said spring rests with a, requisite degree of tension, and so that there may be space in front of said bent portion to receive two other tooth-shaped upwardly projecting pieces 115 and 116 that are formed on the forward end of said escapementspring 112, and which are sustained in jux tapos ition to the upper teeth, but slightly to the rear thereof. A retracting-spring 117, suitably located, holds said armature normally away from the private-magnet polepiece. A well-known auxiliary switching mechanism common to such switches is the so-called side-switch. It is shown in connection with the first-selector A and comprises an arm 118 which is secured to the switch-frame in such a manner that it may be made to swing about a vertical axis that 1,1ea,sse

extremity of said arm is drawn out into a finger 120 that works in conjunction with the escapement teeth previously described. Said teeth, in a manner to be shown, convert the outward 'inovement of the sideswitch, by means of said finger, to a step-bystep motion, which movement is produced by a retracting-spring 121. At the base of the finger 120 a lug 122 that is bent to the front is adapted to strike the cam 38 at a suitable time. Whenever the shaft is rotated, however, said cam is carried beyond the reach of said lug. Near its left extremity the arm 118 carries a number of wipers 123,124, 125 and 126 suitably mounted upon a pin 127 and insulated therefrom and from each other. Said wipers are known as the side-switch-wipers and are adapted to be operated by the private-magnet and escape ment device previously explained. If the private-magnet is energized once the private-armature is drawn down once and restored toits normal position. The escapeinent finger 120 then passes from behind the tooth 115 to the rear of the tooth 113 at the downward stroke of the private-armature 104, and from behind the latter tooth at the return stroke. As soon as the escapement finger clears or disengages the latter tooth the retracting-spring 121 draws the sideswitch to the second position, where it is stopped by the lug 122 when it strikes the cam 38. Im'mediately, then, when the rotary-magnet energizes, the shaft is rotated and the cam passes out of reach of the lug 122. Then the finger 120 of necessity falls against the tooth 116, because of the tension in the spring 121. The rotation of the' shaft results when the rotary-armature 93 is attracted by the rotary-magnet, and at the same time the rotary-armature-finger 102 depresses the private-armature 104 and causes the finger 120 to disengage from the tooth 116 and advance against the tooth 114. Then,as the rotary-armature returns to normal position, when the rotary-magnet deenergizes, the private-armature on following the finger 102 permits the escapement-finger 120 to escape from the last tooth 114, thus permitting the side-switch to pass to the third position with the said finger resting against the side-switch-stop 128. In their normal positions. the side-switch-wipers 123, 124, 125 and 126 engage with the contact points 129, 130, 131 and 132, respectively. This position is known as the first position of the side-switch, at which time, it will be clear, the finger 120 is held behind the escapement tooth 115. In the second position, while the said finger is between the teeth 116 and 115, the said side-switch-wipers engage instead with the contact-points 133, 134, 135 and 136, respectively; and when the said finger 120 falls against the stop 128 the wipers shift their positions into contact with the gontlact-points 137, 138, 139 and 140, respecive y.

Betweenthe pivots 119 and the wiper supportlng pin 127 a rearwardly-extending arm 141 on the side-switch-arm 118 pivotally supports on its 142, the other end of which latter, being bifurcated, engages with the lower end of the double-dog-arm 87 which is constructed somewhat in. the shape of an inverted 1]. Should the release-magnet be energized while the side-switch is in third position, and, of course, while the shaft is rotated, the release-llnk 77, being attached to the release-armature 79, is then thrust. forward when the release-armature is attracted, and catches the lug 88 in the aperture 78. Then,

end one end of a link when said release-armature is restored, the I spring 82, as before described, withdraws the dog 86 from the longitudinal teeth 41. At the same time the arm 87 drives the link 142 back, which latter then rotates the sideswitch-arm about the pivots 119 against the tension of the side-switch retractingspring 121, and thus drives the finger 120 backward between the springs 111 and 112 and into a position behind the tooth 1'15, locking the side switch in the first or normal position. The switch-shaft being unlocked by the removal of the dog 86, and being thus left free, is then rotated by the coil spring 47 until the instant that the end of the shaft-rest enters the slot 43, at which time the shaft then drops to its normal position. Therefore, after the switch has been operated, the energization and denergization of the release-magnet is suflicient to restore the swltch completely to its normal position. The line and private banks are each provided with ten rows of contact terminals, each row consistingof ten sets of contacts, and the shaft is so constructed that it may be raised to any one of ten levels, andat each level it may be rotated ten successive steps in order that the wipers which it carries may .be placed in connection with any one of the ten sets of contact terminals in each level. All parts comprised in circuits are properly insulated in order that they may not come in contact with the switchframe. F or instance, the armatures 53, 54, 59 and 64 are tipped with insulating pieces 143, 144, 145 and 146, respectively, so that the springs which said armatures control may not be grounded on the switch-frame. In like manner the wipers 35, 36 and 37 are suitably insulated from the collars 147 that hold them, which collars are secured to the switch-shaft by means of suitable screws.

The connector C is of matic ringing common battery type, and may be modified if desired, but a standard type is represented in Fig. 3. .The said connector O and the first-selector A are very similar, but in the provision of relays and circuits the two switches are quite different. Like the first-selector A the said connector C is located above the line and private banks 148 and 149, respectively, with which the switch-shaft-wipers 150, 151 and 152 respectively engage. The said wipers, as in the first-selector, are mounted upon a switch-shaft153, which shaft is provided, in addition, with the usual cam 154, longitudinal teeth 155, circular teeth 156, normalpost-arm 157, and coiled spring 158, the

- outer end of which latter is attached to the magnet 17 4 are severally similar to those described in connection with the first-selector and perform similar functions. The re lease-magnet, however, as distinguished from the release-magnet of the first-selector, has its armature 175 located on the right side instead of on the left. Said armature is provided with an elongated. member 176 for controlling the double-dog 177 at the release. Said double-dog is a familiar element and the exercising control of the said release-armature 175 will be hereinafter described. The release-link 178 of the connector, unlike the release-link of the first-selector, is permanently fixed to a suitable part of the switch by the pin 179. Normally said release-link has a downward spring tendency or tension and acts as a latch for retaining the double-dog 177 normally disengaged from the switch-shaft 153, at which time the upwardly projecting pin 180 upon the upper side of the body of the double-dog 177 is retained within the aperture 181 provided upon the right extremity of said release-link 178. The L-shaped .piece 182 upon the under side of the vertical-arm 183 reaches under said releaselink, and whenever the switch is brought into use and at the first upward movement of the said -vertical-arm 183 the said L- shaped piece, as in the first selector, wrenches the release-link from engagement with the pin 180. While the switch is in operation the said release-link is disengaged from the said double-dog 177 and rests with its end upon the pin180 and with the vertical and rotary dogs 184 and 185 in engagement with the shaft 153. The double-dog 17 7 is returned from its operative to its normal position by the release-armature 175 when the release-magnet 172 is energized.

Upon the energization of said magnet the.

elongated portion 176 of the release-armature 175 strikes the double-dog 177 to the right of its bearings 186, so that the pin 180 is driven under the aperture 181 of the release-link 178 and caught therein. The rotary-magnet-armature 187 of the connector is somewhat more simple than that of the first-selector. It is provided with the rotary-arm 188 and with the rotary-pawl 189. The shaft being raised, each time that the rotary-magnet 173 is energized it rotates the switch-shaft one step at a time in the same mechanical manner that the first-selector-shaft is rotated by the first-selector rotary-arm each time the rotary-magnet is energized. The private-magnet 174 is designed to control, in a step-by-step manner, the operation of the side-switch from first to second and from second to third positions, by means of the escapement-teeth 190, 191, 192 and 193 and the escapement-finger 194, which operation results from the retracting tension of the side-switch retracting-spring 195. The private-magnet 174, furthermore, through the medium of the laterally projecting arm 196, controls four privatesprings 197, 198, 199 and 200, so that when thesaid magnet. 174 is energized the former two (197 and 198) of said springs that normally rest in engagement are separated and the springs 198, 199 and 200 that are normally out of contact are closed into contact-that is, when the private-armature is attracted the springs 197 and 198 will be found out of engagement and the springs 198, 199 and 200 in engagement. It will be understood that the connector switch-shaft 153 after being raised and rotated may be restored to normal position together with the side-switch (the latter, of course, being out of normal position) at the energization of the release-magnet 172. The releasemagnet 172 being energized after the switch has been operated, the side switch and double-dog are thrust into normal position by means of the double-dog release arm 201 and the side-switch-link 202, and through the medium of the release-armature member 176, against the tension of the retractingsgrings 195 and 203. At the same time, the s aft being deprived of its locking member (the rotary-dog 185) is rotated by the coiled spring 158 to normal rotary position, which shaft then as usual falls to normal vertical position.

The connector C also has a couple of aux-- iliary-relays 204 and 205 and a couple of differential-relays 206 and 207 for purposes to be disclosed hereinafter. The relay 204 controls by its armature 208 a couple of springs 209 and 210 that are normally in contact with the springs 211 and 212, and the relay 205 by its armature 213 controls a spring 214 that normally engages the spring 215; and when the relay 205 is energized the armature forces the said spring 214 onto the spring 216 and the latter onto the spring 217 but it will -be understood that the spring 215 follows up the spring 214 for a short distance, so that there "comes a tune when the springs 214, 215, and 216 are in contact for a moment. The differential-relay 206 is provided with two windings 21 8 and 219 which are connected with the vert1- cal and rotary line-relays 162 and 163, respectively, which line-relays are 1n turn connected with the main trunk-conductors that lead, as shown in Fig, 1, to the first-selectorbanks 32 and 33. ,Whenever either or both of said trunk-conductors are grounded the said differential-relay 206 becomes energized, but when one is connected to ground and the other to the non-grounded terminal of the central battery B said relay does not energize. The said differential-relay has under its control three springs 220, 221 and 222 of which the springs 220 and 221 are normally in contact, but when the said relay is energized the spring 221 is forced away from the spring 220 and brought into enga ement with the spring 222. Similarly, the di erential-relay 207 is provided with two windings 223 and 224 which are connected with the vertical and rotary line-wipers 151 and 150, respectively. The said relay is so constructed that whenever either or both of the said line-wipers are connected to the ground terminal of the battery B the said relay 207 is then energized, but if one of said wipers is connected to the non-grounded terminal while the other is connected to the grounded terminal of the battery the said relay does not energize. In general, therefore, the windings of either of said differential-relays 206 and 207 if energized in a series circuit, do not energize the relay. The ringer-relay 225 is a feature common to all the connectors of the general type under consideration and has power when magnetized by means ofits armature 226 to disconnect the terminals of the calling line from those of the called line, and to place across the latter the terminals of a ringer-generator 227. This operation is accomplished by means of the said armature 226. and the ringer-relay-spring 228, 229, 230, 231,232 and 233; When said armature 226 is attracted the springs 229 and 232 that normally rest in contact with the springs 228' and 231, respectively, are separated from said springs and pressed into contact with the springs 230 and 233. At the central station and usually upon the shaft of the generator there is provided a circuit-interrupter 234 which when the connector C is operated for certain purposes causes the said ringer-relay to be intermittently energized and denergized.

In Fig. 1 the first-selector A that is asso ciated with the called line is identical with the first-selector A of the calling line and needs no further explanation, since like parts are likewise represented. When reference is made to the parts of said called first-selector it will be understood that their functions and constructions are the I same as those already described for the first-selector 'A. In the particular system shown it will be clear that there may be a multiplicity of substations each of which is connected with the central station by a line of two conductors each of which lines has permanently allotted to it a first-selector. The first-selectors may be subdivided into groups of one hundred each with all suitable li'ne-bank-terminals of a. given group connected in multiple, a similar arrangement being followed in connection with the private-bank-terminals.

For each level of first-selector line-bank-terminals one set of ten trunk-lines is provided, with a connector connected to each one of said trunks. For each level to which a firstselector-shaft may be raised its line-wipers are placed on a level with a different set of connectors for the purpose of reaching subscribers in different hundreds. Each firstselector is connected with a given set of bank-contact-points in the banks of the connectors of the .given hundred to which said first-selector belongs, and when the firstselector comes into use a guarding potential is placed at the connector private-bank-contacts of the line of the calling first-selector to prevent any other calling subscriber from calling this same line. But while a line is idle a connection with said line is made over the trunk-conductors that extend between the connector-banks and the first-selector.

To more fully understand the operations and circuits in connection with my improved system a description will now be given of the circuits brought into use in the system when one subscriber calls another subscriber, for instance, as illustrated in Fig. 1 when the subscriber at substation #100 calls the subscriber at substation #220, which is as follows: The subscriber at the calling substation #100 removes his receiver from the switch-hook 2, and thus causes the groundsprings 20 and 21 to come into contact and to complete a circuit between the ground terminal G and the ground-post 19, through the said springs 20 and 21 andthe conductors 235 and 236. Immediately after, the vertical push-button 26 is pressed twice, then the rotary-button 27 once; again the first button 26 twice, and the second button 27 once, and for the last time the first button ten times, and the last button once. When the spring 30 is forced onto the ground-post 19 twice in succession for the first time, the vertical-line-conductor 237 is grounded twice, causing the vertical-line-re lay 51 of the first-selector to become magnet- 'and raises theswitch-shaft two steps.

minal of battery B to ground G.

cut-ofi-relay-springs 61 and 62 to the battery-lead 239 and to the non-grounded ter- As a result the line-'relay-spring 55 is forced onto the ground-spring 57 twice, which operation closes a magnetizing circuit through the vertical-magnet 67. The current in this second circuit enters the line at the ground terminal G and thenpasses through the springs 57 and 55 to the conductor 240 and through the private-springs 109 and 108 and to the vertical-magnet 67, and to the battery-lead 239 to the non-grounded terminal of battery B and to ground G. The vertical-magnet 67 then attracts the vertical-armature twig:g the firststep, of course, the release-link 77 is withdrawn from the double-dog 83, at which time the dog- 85 engages with the circular teeth 42 and prevents the shaft from falling to its original or normal position. As soon as the switch-shaft rises, the off-normal spring 48 then closes with the grounded contact-point 50, at which instant, and by which act, the connector private-bank-contacts that correspond to the line-conductors of the substation #100 are connected with ground, which connection establishes a guarding potential over said line, so that no subscriber may be able to connect with it after once the first-selector A of said hne has been operated. The vertical-line-conductor being grounded twice, then the pushbutton 27 in turn forces the spring 31 onto the ground-post 19 once and the rotary-lineconductor 241 is grounded once. An electric current then flows through the rotary-linerelay 52 for a moment, which magnetizes the said rotary-line-relay, causing the latter to attract its armature 54 once and force the spring 56 against the ground-spring 57 once. As a result a magnetizing circuit is completed through the private-magnet 103. The electric current in this latter case flows from the ground terminal (3: and thence through the liue-relay-springs 57 and 56 andrconductors 242 and 243 to the private-magnet 103 to the battery-lead 239 and to the nongrounded terminal of battery B and to ground G. The private-armature 104 being attracted once and restored immediately, the escapement-tooth 115 first clears the escapement-finger 120, which latter then falls against the second tooth 113; and when the armature} returns to its normal position this latter tooth also clears in turn the. said escapement-finger. At that instant the sideswitch is drawn into the second osition by the retracting-spring 121 with the cam-lug 122 resting against the cam 38.

.It. will be understood that the prongs of the bifurcated end of the link 142 that rests upon the T'-shaped extremity of the doubledog releasing-arm 87 are of suflicient lengthto permit the said releasing-arm 87 to move from the osition that it holds when the double-do is held normally locked by the release-hut 77 to the position it assumes when the said double-dog is released, without disengaging said prongs.

At the moment that the side-switch passes from the first to second position a circuit 1s completed through the rotary-magnet 90, when the side-switch-wiper 123 closes with the contact-point 133. The current then flows'from the ground terminal G to the contactpoint 133 and through the sideswitch-wiper 123 and conductor 244 to .the rotary-magnet-coil 92, thence througfi'the lnterrupter-springs 100 and 101 and through the second rotary-magnet-coil 91 to the battery-lead and to the non-grounded terminal of battery B and to ground G. The rotarymagnet 90 then attracts the rotary-armature 93 and forces the rotary-pawl 97 into engagement with one of the longitudinal teeth 41, causing the shaft to rotate one step,since said shaft has already been raised. Just at the time, or at the instant before, the rotaryarmature strikes the rotary-magnet polepieces, the rotary-dog 86 falls behind the first of the longitudinal teeth, in the manner already described, to prevent the shaft from returning to its normal osition when the rotary-magnet becomes d eenergized at the instant that the interrupter-finger forces 105 the interrupter-springs apart and destroys the energizing circuit through the said magnet. This interruption occurs just at the time when the rotary-armature strikes the pole-pieces. At the same time that the ro- 11o tary-pawl 97 advances to engage the longitudinal teeth, as described, the rotary-armature-finger comes into contact with the private armature 104, producing a depression of the latter at the same time'that the rotar 115 pawl produces a rotation of the shaft. s the shaft begins to rotate the cam 38 very soon passes out of reach of the cam-lug and permits the escapement-finger 120 to fall against the tooth 116 before the rotary-ar- 120 mature-finger 102 has depressed the private armature 104 too far. Very soon, however, the said tooth 116 is carried below the finger 120, which latter then falls against the upper tooth 114 at about the time that 12 the shaft-wipers are rotated onto the first contact of the second level of their respective banks. As soon as the energizin circuit through the rotary-magnet is interrupted the rotary-armature then begins to return to its normal position, and the private-armature 104 as well, following up the receding movement of the rotary-armature-finger 102. The tooth 114 clears the escapement-finger 120 and the side-switch springs into third position with the escapement-fiuger against the side-switch-stop 128. The shifting of the side-switch takes place just before the interrupter-finger permits the interrupter-springs 100 and 101 to reengage. so that by the time they do reengage the energizing circuit that has been described through the rotary-magnet has been destroyed between the side-sWitch-wiper 123 and the contact-point 133.

When the motion of the rotary-armature ceases permanently the operation of the first-selector comes to an end, the line-wipers 35 and 36 having seized upon an idle trunkline similar to the trunk-line whose conductors 245 and 246 terminate at the tenth set of contacts of the second level of the same line-bank. The seized line is protected from further seizure by a guarding potential at the private-wiper and. therefore, at the first contact of the second level of the privatebank 33, and at all other private-contacts in multiple. Said guarding potential is established by reason of the connection between the grounded terminal of battery B and said private-contacts, through the ground terminal G, side-switch-wiper 124, conductor 247, back-release-relay 63, conductor 248 and the private-wiper 37. Similarly, should any first-selector appropriate to its use the second trunk-line of the same level, a guarding potential will then appear at the second private-contact of the second level of the private-bank 33, as well as at all other private-bank-contacts connected in multiple thereto. And should a third first-selector seize the third trunk-line on the same level a guarding potential will also appear at the third private-contact of the second level, and should the fourth, fifth, etc., and ninth trunks be occupied guarding potentials would be found at the fourth, fifth, etc., as well as at the ninth private-contact-terminals of the second level of the private-bank. Therefore, if the first nine trunk-lines of the second level are busy a guarding potential is found at each one of the first nine privater-ontacts of the second level of the privatebank If this condition exists at the time that the calling subscriber grounds his l'(ltill'YdlIlG-COIldllCtOl by pressing button 27, the rotation of the shaft Will not terminate as soon as the wipers have moved onto the first terminal of the level to which they have been raised. The first nine private-contacts being grounded, then when the calling subscriber grounds the rotary side of the line the side-switch trips into second position in the manner described; but then the rotation of the shaft Will egin, not to cease until the wipers have been carried beyond the last of the busy trunk-lines-in this case onto the tenth terminal of the second level of the banks in question. This operation takes place in the following'manner: The energizing circuit through the rotary-magnet being closed, as was pointed out, at the juncture when the side-switch-wiper 123 engages with the contact-point 133, the rotary-armature is attracted by the rotary-magnet 90, and the shaft is rotated one step in the manner described, so that the line and private wipers are rotated into engagement with the first terminal of the second level of their respective banks. At the same time the privatearmature is depressed by the rotary-armature-finger and the interrupter-springs 100 and 101 at the end of the stroke are separated by the -1nterrupter-finger 99. There being a guarding potential at the first contact which the private-wiper meets, a circuit is completed through the private-magnet 103 which extends from the grounded terminal of the battery B through the private-wiper of whatever first-selector is occupying the first trunk of the second level in question, through the bank-multiplying-conduct0rs to the contact-point with which the private-Wiper 37 has engaged, thence through said privatewiper-conductor 248, winding of the backrelease-relay 63, conductor 247, the side switch-wiper 124, contact-point 134, conductors 249 and 243 and private-magnet 103 to the non-grounded terminal of battery B and to ground G. The private-armature is thereby retained in the depressed condition, even after the energizing circuit is broken at the interrupter-springs, and while the rotaryarmature-finger 102 returns to its normal position in response to the retracting tension of the rotary-armature-spring 95. 'Since the escapement-finger 120 is held by the upper foremost escapement-tooth 114, and since the side-sWitch-wiper 123 is, therefore, retained in engagement with the grounded contactpoint 133, as soon as the interrupter-springs reengage the energizing circuit through the rotary-magnet 90 is completed once more. As a result, the rotary-armature is attracted again, the shaft is rotated one more step, and the private-wiper 37 is moved onto the second terminal of the second level of the private-bank 33. Said second contact also being grounded the energizing circuit through the private-magnet is still maintained so that the side-switch is not liberated when the rotary-armature again returns to its normal position. Clearly, then, the shaft Will be rotated in a step-by-step manner as long as the private-wiper contlnues to encounter grounded private-contacts. After having rotated onto the ninth contact, the private-wiper is rotated one more step and into engagement with the tenth cont-act of the second level of the private-bank; but

this last contact is devoid of guarding potential, and as soonas the said wiper leaves the ninth contact the magnetizing circuit through the private-magnet that has up to this time maintained the private-magnet energized is broken. This occurs at just about the time when the rotary-armature is at the end of its forward stroke, so that the private-armature that has up to this time held the side-switch in its second position, by the magnetizing force that has now disappeared from the private-magnet falls back upon the rotary-armature-finger and follows said finger as the rotary-armature returns to its normal position.

Between the time that the private-armature is released by the private-magnet and the time that the rotary-armature fully regains its normal position, the escapementfinger 120, which, during the rotation of the shaft, has been resting against the foremost tooth of the upper escapement-spring, disengages from said tooth and permits the side-switch to pass to the third position. It is then that the side-switch-wiper 123 leaves the contact-point 133 and passes onto the contact-point 137. This disengagement occurs just before the interrupter-springs 100 and 101 rengage, so that the circuit through the rotary-magnet is permanently broken in order that no further rotation of the shaft may take place during its operation. The side-switch-Wipers 125 and 126 having engaged with the contact-points 139 and 140, the subscribers line-conductors 237 and 241 are thereby extended through the respective side-switch-wipers 125 and 126 and over the conductors250 and 251 to the vertical and rotary line-wipers 36 and 35, respectively. Said wipers are at the time in engagement with the tenth contact of the second level of the line-bank 32 and place the calling subscriber #100 in connection with the connector 0 through the vertical and rotary trunk-conductors 245 and 246. The calling line #100 being thus extended, when the subscriber presses the vertical-button 26 tWice for the second digit he again grounds the vertical-line-conductor 237 twice and thus operates the verticalline-relay 162 of the connector C twice. The energizing current flows from ground G to the ground-post 19, thence through the spring 30, conductor 237, side-sWitch-Wiper 125 of the first-selector A, contact-point 139, conductor 250 vertical-line-wiper 36, vertical-trunk-conductor 245, vertical-line-relay 162 of the connector 0, winding 218 of the differential relay 206 to the battery-lead 239 and to the non-grounded terminal of battery B and to ground G. The vertical-linerelay 162 of the connector 0 then attracts its armature 164 twice and the latter thereby forces the line-relay-spring 166 against the ground-spring 167 twlce. As a result, the

vertical-magnet 171 is energized twice in succession. raising the connector-shaft 153 one step each time by means of the verticalarmature 252 and the vertical-pawl 253. The current through the said vertical-magnet passes from ground G through the linerelay-springs 167 and 166, conductor 254, private-springs 197 and 198, conductor 255, side-switch-n'iper 256. contact-point 257, conductor 258 to the said vertical-magnet 171 and thence to the battery-lead 239 and to the non-grounded terminal of battery B and to ground G. At the first movement of the vertical-arm 183 the releaselink 178 is disengaged from the double-dog 177 by the L-shaped piece 182, and the vertical-pawl 253 then engages one of the circular teeth 156 and so raises the shaft 153 that the vertical-dog 184 catches and holds the said shaft in the raised position, in the manner described in connection with the first-selector A. At the second step of the verticalarmature 183 the shaft 153 is raised another step, in which new position it is retained by the said dog 184. The subscriber having thus raised the connector-shaft and placed the shaft-wipers 150, 151 and 152 opposite the first contact of the second level of the connector-banks, the next presses the rotarybutton 27 once, grounding the rotary-lineconductor 241 as before, and causing thereby an energizing current to flow through the rotary-line-relay 163 of the connector C for a moment. This current flows from ground G at the substation #100 to the groundpost 19, thence over the rotary-line-conductor 241 and through the first-selector sidesWitch-wiper 126, contact-point 140, conductor 251 to the rotary-line-wiper 35, thence over the rotary-trunk-conductor 246 and through the rotary-line-relay 163 and Winding 219 of the differential-relay 206 to the conductor 259 and through the verticalback-bridge-relay-springs 209 and 211 to the battery-lead 239 and to the non-grounded terminal of battery B and to ground G. The rotary-line-relay 163 being thus energized once has its armature 165 attracted once, which forces the springs 16S and 167 into contact. As a result the connector private-magnet 174 is energized by a current which flows from ground G5 through the springs 167 and 168, conductor 260, privatemagnet 174, conductors 261 and 259, vertical-back-bridge-relay-springs 209 and 211 to the battery-lead 239 and to the non-grounded terminal of battery B and to ground G. The private-magnet 174 being energized for the first time the escapement-fingcr 194 clears the escapement-tooth 192 at the downward stroke of the private-armature 262, and clears the upper escapement-tooth 190 at the return stroke.

The side-switch, of course, is brought into Second position and stopped when the lug 263 strikes the cam 154; and the side-switchwiper 256 having left the contact-point 257 is in engagement with the contact-point 264 instead, so that when the subscriber next presses the vertical-button 26 ten times and energizes the vertical-line1-elay 162 ten times the rotary-magnet 173 instead of the vertical-magnet 171 is magnetized ten times. The energizing circuit through the magnet 173 permits current to flow from ground G through the line-relay-springs 167 and 166, private-springs 197 and 198, conductor 255 and side-switch-wiper 256 to the contactpoint 264 and rotary-magnet 173, thence to the battery-lead 239 and to the non-grounded terminal of battery B and to ground G. The rotary-armature 187 is, therefore, attracted ten timesonce each time that the rotarymagnet is energized. Each time that the said armature is attracted, the rotary-pawl 189 engages one of the longitudinal teeth 155 and rotates the shaft 153 one step in the same manner that the first-selector-shaft is rotated. At the first circular step the shaftrest 161 receives the shaft when the verticaldog 184 is drawn out of engagement with the circular teeth 156 at the time that the rotarydog 185 reaches the crest of the longitudi nal tooth over which it has to pass at the time; and by the time that the rotary-armature 187 strikes the rotary-magnet pole-pieces this last dog drops into locking engagement behind the said longitudinal tooth and retains the shaft in its advanced rotary position. At the first circular step the shaftwipers 150, 151 and 152 pass onto the first contact of the second level of their respective banks 148 and 149, at the second step onto the second contact, and so on step by step until they reach the tenth contact of the second level. The last step of the calling subscriber to complete his connection is to again ground the rotary-line-conductor 241 once by pressing the rotary button 27 once. Again the rotary-line-relay 163 is energized and again the private-magnet 174 attracts its armature 262 once. The shaft having been rotated so that the cam 154 no longer obstructs the side-switch-arm 265, the escapenlent-figure 194 at the downward stroke of the private-armature 262 clears the tooth 193, and when the said armature returns toward normal position the upper tooth 191 is also cleared, at which instant the said side-switch springs into third position. The passage of the side-switch to third osition connects the private-wiper 152 with the ground terminal G", when the side-switchwiper 267 passes onto the contact-point 268. This ground connection establishes a guarding potential at the tenth private-contact of the second level of the private-bank 149 that corresponds to the terminal of the normalconductors 269 and 270 of the called subscriber, and at all other private-bank contacts connected in multiple thereto, so that no other subscriber may call in upon said line while the said guarding potential exists.

The calling first-selector, it will be remembered, places a guarding potential at the banks of the connectors of the hundred to Which the subscriber #100 belongs, at the instant that the off-normal spring 48 comes into contact with the ground-spring 50, to prevent any subscriber from calling in upon the line of the calling subscriber. Therefore, neither the calling nor the called subscribers will be interrupted after they are once connected. The establishment of a guarding potential at the tenth contact of the second level of the private-bank 149 not only protects the called line from further seizure, but at the same time forces a current through the bridge-cut-otf-relay 271 of the called first-selector A which relay, by means of its armature, controls the bridgecut-olf-relaysprings 272, 273 and 274. The said relay, when magnetized, separates the said springs from each other and thereby opens a bridge circuit normally established through the vertical and rotary line-relays 275 and 276, across the normal-conductors 269 and 270, and at the same time interrupts a connection between said relays and the non-grounded terminal of battery B, which terminal is directly connected with the spring 272. Since the said normal-conductors are included, one on each side of the main talking circuit, as hereinafter disclosed, it is desirable to remove said bridge from between them, for obvious and other reasons, to obtain the best results. The circuit through the said bridge-cut-ofl'-relay 271 extends from ground Gr to the connector side-switch contact-point 268, sideswitch-wiper 267, conductor 277, privatewiper 152, private-normalconductor 278, spring 279, contact-point 280, bridge-cutoff-relay 271 to the battery-lead 2,39 and to the non-grounded terminal of battery B and to ground G. When the side-switch-wiper 267 passes onto the said grounded contactpoint 268, still another circuit is established which comprises the ringer-relay 225 and the ringer-relay circuit-interrupter 234 in series. This last circuit extends from ground G to the contact-point 268, sidesWitch-Wiper 267, conductor 281, rotaryback-bridge-relay-springs 215 and 214, vertical-back-bridge-relay-springs 212 and 210, conductor 282, ringer-relay 225, circuit-interrupter 234 to the battery-lead 239 and to the non-grounded terminal of battery B and to ground G. The said circuit-interrupter, it will be understood, is constructed somewhat like a commutator with alternate metallic and non-conducting segments in which the diametrically opposite metallic segments are connected dlre'ctly together.

The brushes 283 and 284, furthermore, are arranged to touch the circumference of the circuit-interrupter at points 180 degrees apart and, therefore, the ringer-relay is energized each time the said brushes pass onto the connected metallic segments and is deenergized when they pass onto the insulation. Each time that the ringer-relay 225 is energized the ringer-relay-springs 229 and 232, as stated, are separated from the ringer-relay-springs 228 and 231 and forced onto the springs 230 and 233. These last two springs 230 and 233 constitute the terminals of the ringer-generator 227 which are thereby placed across the line-conductors 285 and 286 of the called subscriber #220. Each time that the ringer-relay circuit-interrupter 234 causes the said ringerrelay 225 to be energized a signaling impulse is sent out to the subscribers line, which impulse occurring intermittently will ring the called subscribers bell 287 intermittently until he answers or until the calling subscriber disconnectsl It will be noticed that each time that the vertical and rotary line-relays 162 and 163 have been energized the circuit comprises one of the windings of the differential-relay 206; but the energizing of said relay heretofore has played a part of no significance. Before going further it will be explained that if for any reason the called line is busy.

at the time that the calling subscriber grounds his rotary-line-conductor 241 for the last time (to transfer the connector sideswitch from second to third position) the guarding potential at the connector privatebank 149 will lock the side-switch in second position, to prevent it from passing to third position, and abusy signaling current is then sent to the calling subscriber to notify him that the connection With the called line has not been made. For instance, after the called line has been called by any connector there will be a guarding potential at the tenth private-contact of the second level of the private-bank 149, corresponding to the line of the called substation #220. Or, on the other hand, if the first-selector A of the called line is in use the same private-bankcontact will be connected to ground for reasons described. The guarding potential, in this case, will reach the said contact-point by way of the 1)rivate-normal-conductor 278. At any rate if the private-wiper 152 finds a guarding potential at the said contact when the calling subscriber #100 grounds the rotary-line-conductor 241 for the last time the connector side-switch is locked in second position and prevented from passing to third position. The explanation of what occurs is as follows: The private-wiper 152 beingconnected to ground at the tenth 'contact of the second level. as stated, when the calling subscriber #100 grounds the rotaryline-conductor by pressing the rotary-button 27 for the last time. the rotary-line-relay 163 is energized, as described. and as a result the private-magnet 174 is energized also. But when the rotary-line-relay 163 deenergizes the private-magnet 174 does not deenergize, because a local energizing circuit is provided elsewhere. The establishment of the said local energizing circuit for the private-magnet 174 is brought about in the following 5 manner: 'hen the privatemagnet attracts its armature 262 the private-springs 198 and 199 are pressed into contact and. therefore, the rotary-back-bridge-relay 205 is energized. The energizing circuit for said rotary-back-bridge-relay may be traced as follows: From the grounded private-bankcontact in question through the privatewiper 152, conductors 277 and 281, rotaryback-bridge-relaysprings 215 and 214, rotary-backbridge-relay 205 (Fig. 3), sideswitch contact-point 289, side-switch-wiper 290, conductor 291, private-springs 199 and 198. conductor 255, side-switch-wiper 256, contact-point 264, rotary magnet 173 to the non-grounded terminal of battery B and to ground G. The rotary back-bridge relay 205 is thus energized through the rotary magnet 173. but since the resistance of said relay 205 is comparatively high as compared with that of the rotary magnet 173, the latter magnet is not energized, since the ampere turns are not sufficient to operatively energize said rotary magnet. At the instant the rotary back-bridge relay 205 attracts its 100 armature 213, a holding circuit is provided for said relay independent of the grounded private bank contact. and at the same time a locking circuit is provided for the private magnet 174 to take the place of the original 10:; energizing circuit through the line relay spring 167 and 168, as described. The holding circuit for the relay 205 extends from ground G through the conductor 293, springs 216 and 214 and thence through the relay 205 and magnet 173 to battery. In order to insure the proper closing of the above circuit, the spring 214 is preferably adjusted so as to engage the spring 216 before it disengages the spring 215. The new 11." holding circuit which is closed through the rivate magnet by the relay 205 extends ii'om ground G throu h the conductor 293,

rotary back-bridge relay springs 216 and 217, conductors 294 and 260, private magnet 174, conductor 261. vertical back-bridge relay springs 209 and 211 to the battery lead 239 and to the non-grounded terminal of battery B to ground G. The private magnet 174 will remain thus locked until the switches are released by the calling subscriber No. 100 and the escapement finger 194. is retained against the upper foremost escapement tooth 191. As long as the private armature 262 is depressed, a busy sigasso I naling current is transmitted to the substation No. 100 of the calling subscriber, the circuit for which current is completed when the private spring 199 engages the spring 200. Just as the signaling of the called substation is dependent upon the automatic periodic energizing of the connector ringer relay 225, so is the busy signal that is trans mitted to the calling sub-station #100. The energizing circuit for the said ringer-relay 225 for signaling, which was described, comprises the ground terminal G and thesideswitch-wiper 267, but the energizmg c1rcu1t during the busy signal, although it comprises first the grounded busy contact and finally the said ground G, vdoes not include the said side-switch-wiper 267, but branches off from the contact-point 268 to the conductor 293, and thence extends to the rotary back-bridge-relay-springs 216 and 214, Vertical-hackbridge-relay-springs 212 and 210 and conductor 282 to the said ringer-relay 225, thence through the interrupter'234 to the battery-lead 239.

The busy current, like the signaling current, is intermittent and is sent through the receiver 13 of the calling substation each time that the ringer-relay is energized. The busy current flows from the ringer-generator to the conductor 295, thence through the ringer-relay-springs 230 and. 229, sideswitch-wiper 296, contact-point 297, conductor 298, private-springs 200 and 199, con--.

ductor 291, side-switch-Wiper 290, contactpoint 289, condenser 299 to the trunk-conductor 246 and through the primary winding 7 to the vertical-trunk-conductor 245, and through the vertical-line-relay 162, winding 218 of the differential-relay 206 to the battery-lead 239, and to the non-grounded terminal of battery B, thence through the said battery to the ground terminal G and to the ground terminal Gr of the condenser 300, and back to the ringer-generator 227. Attention is called to the fact that a subscriber when calling a busy line may retain his lineqvipers 151 and 150 across the normalconductors 269 and 270 of the said line, but since the side-switch-wiper 267 is in second position, and since the rotary-back-bridgerelay 205 is energized and the spring 215 disconnected from all other springs, there is no guarding potential provided at the private-wiper 152 of the connector C under discussion. calling subscriber may leave his connector in the position described, after he receives the busy signal, Without interfering in the least with other subscribers that may desire to call the line after the original guarding potential is in the meantime destroyed. That is, if subscriber X is connected with the subscriber #220 at the time that subscriber #100 calls and gets a busy signal, and the subscriber #100 does not restore his It will be evident then that the switches, the subscriber number X may dis-' spring 197 (that is connected to the line-relay-spring 166) from the spring 198, so that no subsequent impulses that may be sent over the calling line will operate the connector C and cause its Wipers 150 and 151 to pass onto any other contact. ing subscriber #100 hears the busy signal, and if he restores his receiver to the switchhook 2, he will ground the vertical and rotary line-conductors 237. and 241 simultaneously by forcing the release-springs 22, 23 and 24 into contact. Therefore, the vertical and rotary line-relays 162 and 163 of the connector C will be energized simultaneously. The ground impulse to the vertical line, at the release, is sent from ground G to the release-spring 22, thence through the springs 23and 24 to the line-conductor 237, and thence through the vertical-linerelay 162 and Winding 218 of the differential-relay 206 to the battery-lead 239 and to the non-grounded terminal of battery B. The ground impulse in the rotary-line-conductor 241 is sent from ground G also to the said release-spring 22 and the spring 23, and to the rotary-line-conductor 241, thence through the rotaryv-line-relay 163, winding 219 of the differential-relay 206 and springs 209 and 211 of the vertical-back-bridge-relay 204 to the battery-lead 239, and to the nongrounded terminal of battery B and to ground G. The differential-relay is here energized at the same time that the trunk-release-springs 169 and 170 of the connector C are brought into contact, and as a result the release-magnet 172 of the connector'is energized in series with the back-release-relay 63 of the firs't-selector. The current in this circuit is made to flow from the ground terminal G at the first-selector side-switch to the contact-point 138 and side-switch- Wiper 124, thence through the back-release relay 63 and private-wiper 37 to the trunkrelease-conductor 301, to the connector trunk-release-springs 169 and 170, releasemagnet 172 and difl'erential-relay-springs 222 and 221 to the battery-lead 239, and to the non-grounded terminal of battery 13 and to ground G. As a result the connectorshaft 153 and side-switch are restored to normal position at the same time that the first-selector back-release-relay 63 is energized. When the connector-wipers leave their engaging bank-contacts the energizing circuit through the cut-ofi-relay 271 of the first-selector A of the called line is destroyed. hen this last energizing circuit the prig which latter upon attracting its armature causes the release-link to latch the double- (lllg 83. I

When the'switch-hook 2 at the substation of the callingsubscrlber clears the release-springs the line-relays 162 and 163;

of the connector C and the differential-relay 206 become deenergized, and as a result the release-magnet 172 of the connector, together with the release-magnet 80 of the first-selector permit their armatures to regain their normal positions, at which time the first-seleotor-shaft 34 and side-switch are restored also. But, as previously described, the calling subscriber by connecting with the called subscriber causes his signaling apparatus to be rung. The signaling current passes through the ringer 287 at the called substation over the following circuit: from the ringer-generator 227 to the conductor 302, and through the ringer-relaysprings 233 and 232 to the side-switch-wiper 303, contact-point 304, conductor 305, winding 223 of the diiferential-relay 207, conductor 206, vertical linewiper, 151, vertical normal -'conductor 269, vertical lineconductor 285, condenser 307, ringer 287, ringer circuit springs 308 and 309, rotary line conductor 286, rotary normalconductor 270, rotary-line-wiper 150, conductor 310, winding 224 of the differentialrelay 207, conductor 311, contact-point 312, side-switch-wiper 296 and ringer-relaysprings 229 and 230 to the conductor 295 and back to the ringer-generator 227. The latter subscriber upon hearing the signal will remove his receiver 313 from the switch-hook 314. As soon as he does so an energizing circuit is established through the transmitter 317 and primary winding 315 of thecalled substation, in series with the windings 223 and. 224 of the differential relay 207, and with the vertical and rotary back-bridge-relays 204 and 205. The current in this circuit flows from the ground terminal G at the connector side-switch to the contact'point 268, side switch wiper 267, rotary-back-bridge-relay-springs 215 and 214 to the said rotary-back-bridge-relay 205, thence to the conductor 288, ringer-relaysprings 228 and 229, side-switch-wiper 296, contact-point 312, conductor 311, winding 224 of the differential-relay 207 conductor 310, rotary-line-wiper 150, rotary-normalconductor 270, rotary-line-conductor 286, primary winding 315 of the induction-coil 316, transmitter 317, primary circuit springs 318 and 319, vertical-line-conductor 285, vertical-normalsconductor 269, vertical-linewiper 151, conductor 306, winding 223 of In this circuit the back-bridge-relays 204 and 205 become energized, but the differentialrelay 207. does not become energized.

When the vertical-back-bridge-relay 204 is energized it accomplishes two results: The energizing circuit through the ringer-relay 225 is permanently destroyed when the spring 210 leaves the spring 212, so that no further ringing impulses may be sent over the called line, and the rotary side of the main line is shifted from engagement with the nongrounded terminal of the battery B into engagement with the grounded terminal of the battery B when the spring 209 leaves the spring 211 and passes into contact with the spring 212. The rotary-back-bridgerelay 205 accomplishes but one object during its energized condition at this time: It shifts the path over which the spring 214 establishes connection with the ground terminal G. It will be noticed, however, that the shifting is done without at any time breaking the connection between the said spring 214 andthe ground, since the spring 215 follows up the spring 214 until after the said spring 214 engages the spring 216. though finally the spring 217 comes into engagement with the spring 216 it is a matter of no consequence at this stage. The action of the vertical-back-bridge-relay 204 as a pole-changing-relay in shifting the spring battery onto the grounded spring 212, and the action of the relay 205 in maintaining the said ground connection, provides the calling substation #100 with energizing current for the primary winding 7 of the induction-coil 8 and for the transmitter 9. The current in this circuit flows from ground G at the connector side-switch to the contact-point 268, conductor 293 to the rotary-back-bridge-relay-springs 216 and 214 and to the vertical-back-bridge or polechanging-relay-springs 212 and 209, conductor 259, winding 219 of the differentialrelay 206, rotary-line-relay 163, rotarytrunk-conductor 246, first-selector rotaryline-wiper 35, contact-point 140, side-switchwiper 126, rotary-line-conductor 241, primary winding 7 of the induction-coil 8, transmitter 9, vertical-line-conductor 237, side-switch-wiper 125, contact-point 139, vertical-line-wiper 36, vertical-trunk-conductor 245, vertical-line-relay 162, winding 218 of the differential-relay 206, to the battery-lead 239 and to the non-grounded terminal of battery B and to ground G. The

.209 from the non-grounded terminal of the subscribers #100 and #220 being thus conneeted and their transmitters 9 and 317 be ing thus energized in series with their re spective primary windings 7 and 315, and their respective receivers 13 and 313 being connected in series with the secondary windings 14 and 321, they may now eounmulicate with each other in a well -hnown manner. The path of the voice-c1u-rents between the two substations may be traced as follows: from the transmitter 9 of the calling substation :;':/:100 to the vertical-line-conductor 237 through the first-selector side-switchwiper 125 and vcrtical-line-wiper 36, condenser 322, ringer-relay-springs 231 and 232, side-switch-wiper 303,-winding 223 of the difi'erentialqelay' 207, vertical-line-Wiper 151, vertical-normal-conductor 269, verticalline-conductor 285, transmitter 317, primary winding 315, rotary-line-conductor 286, rotary-normal-conductor 270, and rotary-linewiper 150, winding 224 of the differentialrelay 207, side-switch-wiper 296, ringer relay-springs 229 and 228, condenser 299, rotary-trunk-conductor 246, rotary-linewiper 35, side-switch-wiper 126, rotary-line conductor 241 to the primary winding 7 of the induction-coil S and back to the transmitter 9.

The two subscribers having communicated, the subscriber at the called substation #220 (if the calling subscriber delays in releasing the connector from across his line) may release by hanging his receiver 313 upon the switch-hook 314. As the switchhook descends the vertical and rotary lineconductors 285 and 286 will be grounded simultaneously for a moment, and as a result the rotary-back-bridge-relay 205 is deenergized while the differential-relay 207 is energized. The deenergizing of the rotaryback-bridge-relay occurs because the said relay is short-circuited through ground. The short-circuit includes the ground terminal G at the connector, side-switch contactpoint 268, conductor 293, springs 216 and 214, coil 205, ringerrelay-springs 228 and 229, winding 224 of the differential-relay 207, rotary-linewiper 150, rotary-normalconductor .270, rotary-line-conductor 286, release-springs 324 and 323 to ground G The winding 224 of the differential-relay 207 being thus short-circuited the current through said Winding 224 is cut ofl and as a result the differential-relay is unbalanced and becomes energized. The energizing circuit through the said differential-relay 207 is from ground G through the releasesprings 323, 324 and 325 to the vertical-lineconductor 285 and through the winding 223 of the said differential-relay 207 to the vertical-back-bridge-relay 204 and through the springs 220 and 221 of the differential-relay 206 to the battery-lead 239 to. the nongrounded terminal of battery B and to nector release-magnet 172 is energized inseries with the first-selector back-releaserelay 63 through a circuit in which current flows from the ground terminal G at the first-selector side-switch through the backrelease-relay 63, thence through the connector trunk-release-springs 169 and 170 and release-magnet 172 and springs 327 and iii:

326 to the battery-lead 239, and t0 the nongrounded terminal of battery B and to ground G. As soon as the connector release-magnet 172 is energized the connector side-switch and switch-shaft 153 are relstored and as a result the switch-shaftwipers 150, 151 and 152 of the connector C are withdrawn from the tenth contact of the second level of their respective banks 148 and 149, with the result that the bridge-cutoff-relay 271 is deenergized along with the differential-relay 207 and the vertical-backbridge or pole-ehanging-relay' 204. The consequence is that the energizing circuit through the connector release-magnet 172 and first-selector back-release-relay 63 is destroyed and all parts of the connector as well as of the first-selector resume their normal positions. Having thus disconnected the connector C from his own line the called subscriber #220 as a result has also restored his first-selector A whereby he may, if he chooses, make a call. If, however, the calling subscriber is the one to restore his receiver first the vertical and rotary lineconductors 237 and 241 are grounded in the usual way and the primary result is that the rotary-line-relay 163 is denergized and the differential-relay 206 energized, since the Winding 219 of the latter and the said rotary-line-relay 163 are short-circuited. Comprised in said short-circuit are the ground terminal G at the connector sideswitch, the rotary-back-bridge-relay-springs 216 and 214, the vertical-back-bridge-relaysprings 212 and 209, winding 219 of the differential-relay 206, rotary-line-relay 163, and rotary-line-conductor 241 and the ground-terminal G at the substation #100. Upon becoming denergized the rotaryline-relay 163 permits the trunk-releasesprings 170 and 169 of the connector C to be disengaged and at the same time the differential-relay 206 forces the spring 221 from the spring 220 and into engagement with the spring 222. lVhen the. said spring 221 leaves the spring 220 the vertical-backbridge-relay 204 is deenergized, which latter permits the springs 209 and 210 under its control to return to normal position. As a result the lead from the winding 219 of the differential-relay 206 is re-connected, when the springs 209 and 211 reengage, with the non-grounded terminal of battery B. As a result the rotary-line-relay 163 is re'nergized and the differential-relay 206 release-springs at the substation separate.

It will be evident that in a large exchange where second-selectors are required, secondselectors of the trunk-release type may be employed. When a connection is established their position in a circuit is between the firstselector and the connector, and in this case the third trunk-release-conductor 301 instead of terminating in the first-selectorbanks terminates instead in second-selectorbanks. Said second-selectors are almost identical with the first-selector, save that the normal-conductors and the bridge-cut-oifrelay are omitted. In addition the line-relays are provided with two trunk-releasesprings similar to the trunk-release-springs 169 and 170 ofthe connector C. Thebackrelease-relay is provided with two springs, one connected to one of said trunk-releasesprings and the other to the other, whereby energizing the back-bridge-relay will act the same as energizing both the line-relays. Furthermore, if the system is sufiiciently large to necessitate second-selectors between the first-selector A and the connector C, said second-selectors in such a position would find no use for the bridge-cut-oif-relay and the normal-conductors that terminate in the side-switch wipers 125 and 126. Also, it may be stated that if an exchange is very small it will not be necessary to employ selectors at all. In that case, the subscribers lineconductors would terminate directly in the connector 1ine-relays-that is, the line-conductors 237 and 241 of Fig. 1 would be connected directly to the conductors 245 and 246, respectively, as shown in Fig. 4. Another change that would be necessary for such a small exchange would be the direct connection of the trunk-releasespring 169 to the ground terminal G as shown in said figure. Upon the release, both line-relays would be energized and the release-magnet 172 shown in Fig. 3 would be energized in a familiar manner.

I, therefore, provide an automatic common battery telephone system comprising an automatic ringing connector in which there are two differential-relays 206 and 207, one to act as a back-release-relaythat 1s, as a means whereby the called subscriber .may disconnect any line from his own-- and the other a front-release-relay, whereby the calhng subscriber, after the called subscriber has answered, and, therefore, after talking battery current has been supplied to both hnes, may release the switches. I provide a connector in which the side-switch is locked in second osition when the connector calls upon a usy line, and which uses the ringer-generator as a busy signaling machine. I provide, furthermore, in said connector a private-magnet with an energizing circult controlled by the rotary-back-bridgerelay 205 and the said back-bridge-relay w1th a clrcuit controlled b the privatemagnet and by the private-wiper of the connector, whereby when the private-magnet is energized after the private-wiper is on a busy contact the said rotary-back-bridge-relay 1s energized and a new permanent circuit -during the busy lock-out substituted for the other circuit of the private-magnet, and at the same time a local and permanent circuit is established for the said' rotary-backbridge-relay, including springs under the control of said back-bridge-relay itself. I provlde, also, an automatic energizing circult for the connector ringer-relay, comprising a couple of s rings under the control of the vertical-bac -bridge-relay, a couple of springs under the control of the rotary-backbridge-relay, and one of the connector sideswitch-wipers; said circuit being established when the said side-switch-wiper, upon passing to third position, engages a grounded contact-po1nt,'and said circuit being interrupted by said back-bridge-relays whenever they are energized. I provide a busy signaling circuit comprising a condenser connected from one terminal of the ringergenerator to ground and the central battery as well as other features of improvement shown and described. These and other advantages and uses of my novel features and combinations will be obvious to those skilled in the art.

It will be understood, of course, that the resistance of the different coils of the relays and magnets can be adjusted or varied to suit the requirements of different cases, with a view to obtaining the mode of operation described. For example, I have ob tained good results by adjusting the resistance as follows :the rotary and vertical linerelays 162 and 163 one hundred ohms each; the windings 218 and 219 of the differentialrelay 206 two hundred and fifty ohms each; the vertical-back-bridge-relay 204 three hundred and fifty ohms; the rotary-backbridge-relay 205 three hundred and fifty ohms; the private-magnet 174 one hundred and seventy-five ohms; the release-magnet 172 sixty ohms; the vertical-magnet 171 sixty ohms; the rotary-magnet 173 sixty ohms; and the ringer-relay. 225 five hundred olnns. The battery B can be of fifty volts.

During conversation, talking current is fed to the line of the subscribers through the coils of the line-relays and the back-bridgerelays of the connector, as well as through the difierential-windings of the relay 206.

The said line-relays 162 and 163 and the said back-bridge-relays 204 and 205 are preferably of sutlicient self-induction to enable them to act as impedance to prevent the passage of voice-currents through the battery. Obviously, however, the windings of the differential-relay 207 must have as little selfinduction as possible, in order to permit the passage therethrough of the voice-currents traversing the talking circuits.

W'ith my improved arrangement, the calling subscriber merely calls the desired number, leaving the connector to do the ringingthatis, to apply the call-signal to the called line, thus making it unnecessary to employ ringing-keysor push-buttons at the substations. Each connector is adapted to lock itself upon the called line, regardless of whether such line is busy or idle, until the calling subscriber hangs up his telephone, or until the connection is released in some other manner. When a connector locks itself upon a busy line it does so in such manner as to preclude the calling subscriber from listening-in on the conversation already being carried on over such line. At the same time, the connector automatically directs the current from the ringing-generator onto the calling line in such manner as to give the busy signal to the calling subscriber. As explained, the locking of the connector on a busy line does not interfere with the use thereof by the subscriber or subscribers already in possession of such line. lVhen a connector locks itself upon a busy line, and if the calling subscriber should fail to hang up his receiver, the connector could stay thus locked without making the line busy (the subscribers line with which it has attempted to make connection), and Without preventing the subscriber of this line from calling other subscribers and wvithout preventing other subscribers from calling in on such line. The connector by its mechanism, and through the medium of the ringing-generator, will automatically ring or call the called subscriber until the latter answers, or until the calling subscriber hangs up his telephone, providing, of course, that the called line was not found to be busy.

By back-bridge-relays I mean the relays, for example, which are in bridge at the right of the condensers 322 and 299. The line-relays 162 and 163 are front-bridge relays. The expression back-bridge is employed because the relays are in bridge TLW at a point back of the said condensers relatively to the calling subscriber. The expression front-bridge is used because the relays of this bridge are-located in front of the said condensers relatively to the calling subscriber. In other words, a bridge which is at the side of the condensers toward the calling subscriber is known as a frontbridge, while any bridge which is at the side of the condensers away from the calling subscriber is known as a back-bridge. It will be understood, of course, that condensers or any other suitable inductive connections can be employed for thus separating the frontbri-dge or bridges from the back-bridge or bridges.

What claim as my invention is:

1. In a telephone system, a calling subscribers line, a called subscribers line, means whereby said called line is busy or occupied, and a connector for connecting the calling line with the called line, adapted to distinguish between busy and non-busy lines, provided with a ringer-relay, a busy-signal circuit for the calling subscribers line, a busy-signal transmitter comprising a ringergenerator common to all subscribers, a circuit-interrupter common to all subscribers, and an energizing circuit for said ringerrelay, controlled by said circuit-interrupter, whereby each time the ringer-relay is energized current from the ringer-generator is sent through the busy-signal circuit to the calling subscribers station.

In a telephone system, a calling subscribers line, a called subscribers line, a common battery, and a connector for connecting the calling line with the called line, a ringer-generator common to all subscribers, adapted for providing all ringing or signaling current, having one terminal connected to ground, and a busy-signal circuit for the calling subscriber, comprising said ringer-generator and the said ground terminal and the common battery.

3. In a telephone system, a calling subscribers line, a called subscribers line, means whereby the called line is already occupied or busy, and a connector for connecting the calling line with the called line, said connector adapted to distinguish between busy and non-busy lines, and provided with a three-position side-switch, a private-wiper, a busy-signal circuit for the calling subscribers line, a ringer-generator common to all subscribers, a ringer-relay individual to the connector, and a circuit-interrupter for controlling the said ringer-relay, the said busy-signal circuit established when the connector attempts to connect the calling line with the called line, while the side-switch is in second position, closed each time that the said interrupter energizes the ringer-relay, and including said ringer-generator and contacts of said side-switch. 

